The present invention relates to the art of winding equipment. More specifically, the invention relates to an apparatus and a method of producing rolls of plastic bags, in which the bags are wound into a roll without being connected to one another. The invention also concerns a winding station.
Many different types of winding machines are known for winding pliable strips of material such as plastic bags. One type of apparatus is arranged to wind bags into a roll without the bags being connected to one another. In this apparatus, a bag is separated from a continuous web of bag material having transverse lines of perforations in the boundary between adjacent bags. A leading end of the separated bag is arranged to overlap a trailing end of a preceding bag, thereby building a strand of so-called interleaved bags. This strand of bags is then wound into a roll in a winding device.
A roll-forming apparatus of this kind, disclosed in U.S. Pat. No. 5,377,929, has a tumbler assembly, which is arranged between a feeding device and a winding device. The tumbler device is adapted to receive a continuous web of bag material from the feeding device. By rotation of the tumbler assembly, a bag is separated from the web and arranged to partly overlap a trailing end of the succeeding web fed from the feeding device. The strand of interleaved bags thus formed is fed to the winding device, in which a roll of bags is formed.
U.S. Pat. No. 4,000,864 discloses a roll-forming apparatus in which a gripping device is arranged between a feeding device and a winding device. The gripping device is adapted to grip the leading edge of a separated bag as received from the feeding device, accelerate the separated bag relative to a preceding bag, decelerate the separated bag and place a leading end of the separated bag on a trailing end of the preceding bag. This operation is repeated to form a strand of interleaved bags, which are fed to the winding device.
U.S. Pat. No. 4,034,928 discloses a roll-forming apparatus having a sheet tuck-in means in the form of a blade. In this apparatus, separate bags are fed to the tuck-in means, where a bag is folded by advancing the blade into contact with the bag about midway between its terminal edges. Then a succeeding bag is fed to the tuck-in means, folded and advanced such that it is caught between the terminal edges of the preceding bag. Thus, a strand of interleaved bags is created. This strand is fed to a winding device, in which a roll of bags is formed.
One drawback of the above types of apparatus resides in their inherent mechanical complexity. Thus, the prior-art roll-forming apparatus tend to be expensive, have much down-time and require frequent maintenance. Further, the apparatus often include sophisticated control systems for adequate timing of the feeding and overlapping operations. Expensive and delicate sensors might also be installed to provide the necessary timing signals. Also, the overlapping operation often calls for a periodic and abrupt change in the speed of various feeding mechanisms, leading to increased wear and tear in the machinery.
Further prior art is disclosed in U.S. Pat. No. 5,779,180, WO 97/33744 and DE-A-37 42 994, the latter disclosing a device for producing a stack of plastic bags. The stacking device includes a rotating barrel drum, the periphery of which has a projecting needle. Separated bags are sequentially fed to the barrel drum, where they are threaded onto the projecting needle, thereby creating a stack of overlapping bags on the periphery of the drum. By stopping the drum and retracting the needle, the stack of bags can be transferred to a subsequent discharge device.
In U.S. Pat. No. 4,757,952, a winding device is disclosed in which an endlessly rotating belt is used to feed bags onto a winding core where they are wound into a roll.
All of the above-mentioned winding devices suffer from the disadvantage of having to be stopped for removal of a completed roll of bags before winding of a new roll can begin. This causes interruptions in the production, which, in turn, cause increased costs.
One object of the invention is to solve or alleviate some or all of the above problems associated with prior art. More specifically, it is an object of the invention to provide a roll-forming apparatus of simple structure, which is capable of winding bags into a roll without the bags being connected to one another and without inflicting any damage to the bags.
Furthermore, the apparatus should cause low wear and tear to the included components.
A further object is to provide a roll-forming apparatus with little need for control and timing in the production of rolls of bags.
Still another object is to provide an apparatus allowing little down-time and high production rates.
An additional object of the invention is to provide an apparatus capable of being included in or operated together with conventional bag-making machines.
A specific object is to provide a new winding station, which is improved over prior art.
Another object of the invention is to provide a method of producing rolls of bags, remedying some or all of the drawbacks discussed above.
These and other objects and advantages of the invention, which will appear from the description below, are achieved by an apparatus, a winding station and a method as set forth in the independent claims, preferred embodiments and variants being defined in the dependent claims.
The invention is based on the understanding that it is possible to dispense with the arranging of the separated bags in an overlapping fashion before winding them into a roll of bags. Instead, the feeding means is arranged to feed bags one by one to the winding stations. Each winding station includes a rotating spindle, which is arranged to engage with each bag, directly or via bags previously wound thereon, to form the roll of bags in which the bags are unconnected to one another yet firmly held together. This allows a considerably simplified construction of the apparatus. Since the bags are fed one by one to the winding stations, there is no need for tumbling or reciprocating devices manipulating the leading or trailing ends of each bag. This results in a reduced risk of damage to the bags, as well as low wear and tear in the construction itself. Further, since the bags are fed one by one to the winding stations, it is easy to direct the flow of separate bags between different winding stations. This allows high production rates since two or more winding stations can be operated sequentially such that a roll of bags is being formed in one winding station while a finished roll of bags is being discharged from an adjacent winding station.
The apparatus preferably comprises a separation device arranged to separate the bags from a continuous web of bag material with perforations in the boundary between adjacent bags. This provides a rational manner of feeding separate bags to the apparatus.
In one embodiment of the apparatus the separation device includes a first driven pair of rollers for feeding the web, and an engagement means which is arranged upstream of the first pair of rollers, in the feeding direction. The engagement means is operable to engage the web at least intermittently to thereby separate a bag therefrom. This is a practical way of separating bags from the web.
The distance between the engagement means and the first pair of rollers is preferably adjustable to exceed the mutual distance between successive perforations in the web. This provides the possibility of adjusting the separation device to different bag lengths.
The engagement means may include a second driven pair of rollers for feeding the web. In such case, the feeding rate of the first pair of rollers should exceed the web feeding rate of the second pair of rollers. As a result, bags may be separated from the web of bag material without any interruption in the web feeding.
The feeding means of the apparatus according to the invention preferably comprises at least one driven pair of rollers for feeding a bag to the spindle. The bag feeding rate of this pair of rollers essentially corresponds to a web feeding rate of the first pair of rollers of the separation means. This provides a smooth feeding process.
According to one embodiment of the invention, each winding station comprises an abutment means, which is abuttingly arranged on a. major portion of the periphery of the rotating spindle. The bags received from the feeding means are engaged between the abutment means and the periphery of the spindle. This provides a simple way of holding the bags against the spindle.
The abutment means preferably extends over at least ⅔ of the periphery of the spindle. As a result, the bags are securely held against the spindle.
In order to achieve a neatly formed roll of bags, the abutment means is arranged to apply essentially constant force on the roll of bags during formation thereof on the periphery of the spindle.
The abutment means preferably comprises at least one movable endless belt, which is arranged to partly encircle the spindle. This is a mechanically simple way of providing an abutment means.
The belt of the abutment means should be driven at an essentially constant speed in order to feed the bags smoothly onto the spindle.
An effective way of driving the belt of the abutment means is by engagement with the spindle.
In one embodiment of the apparatus, each winding station comprises a guide means arranged to guide the belt during movement thereof. This prevents the belt from moving sideways during movement.
The belt guiding means may comprise a body defining a trench having the shape of an arc. The belt is received in the trench in which perforations are provided in a bottom surface. The perforations are connected to a gas supply device to provide a gas layer between the belt and the bottom surface. The trench prevents the belt from slipping and the gas layer reduces friction between the belt and the trench.
The bottom surface of the trench is preferably formed on a peripheral portion of a cylinder, which is fixedly connected to a support of the winding station. Two opposite wall surfaces of the trench are formed by portions of gables, which are arranged at opposite ends of the cylinder. The fixed connection between the cylinder and the support: of the winding station simplifies the connection of the cylinder to the gas supply.
In one embodiment, the gables are journaled for free rotation relative to the cylinder, thus reducing friction between the belt and the trench.
Each winding station may comprise haul-in means arranged to engage a leading end of a bag with the rotating spindle. This makes for a secure formation of a roll of bags.
In one embodiment of the apparatus of the invention, a first backup roller is arranged against the belt upstream of the rotating spindle, as seen in the direction of belt movement, and a second belt backup roller is arranged against the belt upstream of the rotating spindle, the backup rollers guiding the belt around the rotating spindle. In a region between the first belt backup roller and the spindle, the belt forms a bag haul-in means. As a result, the belt is securely guided around the spindle and an effective haul-in means is provided.
Preferably, at least part of the feeding means is movable relative to the winding station such that, during formation of a roll of bags on the spindle, an essentially constant angle of attack is achieved between a leading end of a bag fed thereto and the haul-in means. This minimizes changes in the flow path of the bags during the roll-forming process.
In one embodiment of the invention, the second belt backup roller has a smaller diameter and is arranged closer to the rotating spindle than the first belt backup roller. The inlet opening defined by the first and second backup rollers can thus be kept small, ensuring that the leading ends of the bags follow the periphery of the spindle.
The first and second belt backup rollers and at least part of the feeding means may be arranged at a fixed mutual distance on a movable element, an essentially constant distance being maintained between the movable element and the roll of bags during formation thereof. This provides a way of maintaining an essentially constant force on the roll of bags during the roll-forming process.
According to a preferred embodiment, the rotating spindle is essentially circular in cross section and has a variable diameter. Thus, by reducing the diameter of the spindle, removal of a roll of bags can be facilitated.
An effective way of providing a variable diameter of the spindle is to arrange an interior chamber inside the spindle. The diameter can be varied by changing a gas pressure in the chamber. The change of diameter can also be achieved mechanically.
Further, the spindle may comprise an elongate body, a tube means of flexible material arranged in a number of turns around the body, and a protective sheet covering the tube means and forming a periphery of the spindle. By changing the gas pressure in the interior chamber of the spindle, the tube means effects a change of the diameter of the spindle. The protective sheet provides a smooth surface.
According to a particular aspect of the invention, an improved winding station is provided.
The winding station of the invention comprises a switch means which makes it possible to direct bags into the winding station for forming a roll of bags and to direct the bags past the winding station if the roll of bags in the winding station is completed. In this manner, bags can be directed to another winding station in a series of winding stations while a completed roll is being removed from the first winding station. This means that interruptions in the production are avoided.
According to one embodiment, the winding station of the invention is adapted to receive bags from a feeding means comprising a conveyor belt, and the switch means comprises means for diverting the conveyor belt into contact with the winding station. The diversion of the conveyor belt is a simple way of directing the bags into the winding station.
The switch means preferably comprises a pivotable arm, which is connected to a roller. The arm is pivotable to bring the roller into engagement with the conveyor belt for diverting the conveyor belt upwards. This arrangement makes it possible to easily switch between winding stations when a roll of bags is completed in one winding station.
In a preferred embodiment, the winding station is disposed to be arranged above the conveyor belt, giving the possibility of arranging several winding stations in a row.
The winding station may comprise a haul-in means arranged to move a bag from the conveyor belt into the winding station and to engage a leading end of the bag with the rotating spindle. Thus, a secure transfer of bags from the feeding means onto the spindle is achieved.
According to a further embodiment of the invention, the haul-in means is arranged to move the bag from the conveyor belt into the winding station in a direction which is perpendicular to a feeding direction of the conveyor belt. This makes it possible to easily arrange a number of winding stations above the conveyor belt.
The haul-in means preferably comprises an endless belt, which is arranged to be brought into contact with the conveyor belt when the conveyor belt is diverted into contact with the winding station. This is a mechanically simple way of providing a haul-in means.
According to another aspect of the invention an improved winding apparatus is provided, comprising at least two of the winding stations of the invention.
According to the method of the invention, bags are wound into a roll in one of at least two winding stations, without being connected to one another, fed one by one to a rotational means and wound thereon. When one roll of bags is completed in one of the at least two winding stations, the bags are directed to another of the winding stations. This provides an effective way of forming rolls of bags, as it makes it possible to remove a finished roll while another is being formed.